Zeit- und ortsaufgelöste Beobachtung von Magnetisierungsdynamik unter Verwendung von "Spin-polarized low energy microscopy" (SP-LEEM)

我们将利用自旋极化电子的后向散射截面的磁化依赖性，提供高强度的反射电子和高不对称性。使用发射电子显微镜，我们能够以高于25 nm的高横向分辨率成像磁畴。该技术的一个基本优势是，它结合了高分辨率的磁成像和结构成像，甚至包括表面上单个单原子台阶的可见性。时间分辨率是通过脉冲电子束对样品的频闪照明来实现的，而脉冲电子束又是通过将来自激光二极管的脉冲激光照射到砷化镓光电阴极上而产生的。时间分辨率受电子束脉冲的脉冲长度限制。超快磁化动力学将在样品中通过使用条带线技术的场脉冲或使用钛蓝宝石激光的加热脉冲来启动。我们将研究在超高真空中分子束原位沉积制备的单晶超薄磁性薄膜。从单晶Mo(110)膜在蓝宝石(11-20)衬底上光刻制备条纹线。带状线表面将在超高真空中进行清洁，采用氧退火/闪光循环，以允许超薄Co和Fe薄膜的外延生长。动态磁化过程将作为场和/或加热脉冲相对于电子探测脉冲的时间延迟的函数来研究。

We will exploit the magnetisation dependence of the backscattering cross section of spin-polarised electrons providing both a high intensity of reflected electrons and a high asymmetry. Using an emission electron microscope we are able to image magnetic domains with high lateral resolution of better than 25 nm. A basic advantage of the technique is that it combines the highly resolving magnetic imaging with structural imaging including even the visibility of single monoatomic steps on surfaces. Time resolution is implemented by a stroboscopic illumination of the sample by a pulsed electron beam which in turn is produced by shining a pulsed laserbeam from a laserdiode on a GaAs-photocathode. The time resolution is limited by the pulse length of the electron beam pulse. Ultrafast magnetisation dynamics will be initiated in the sample either by application of field pulses using the strip-line technique or heating pulses using a Ti-sapphire laser. We will investigate single crystalline ultrathin magnetic films prepared by molecular beam deposition in situ in UHV. Strip-lines are lithographically prepared on a sapphire(11-20) substrate from a single crystalline Mo(110) film. The strip-line surface will be cleaned in UHV applying oxygen - anneal/flash cycles in order to allow for an epitaxial growth of ultrathin Co and Fe films. The dynamical magnetisation process will be investigated as a function of the time delay between field and/or heating pulse with respect to the electron probe pulse.